This project aims to improve the evidence base for the AHCPR Unstable Angina Practice Guideline, which challenges clinicians to consider outpatient management for low-risk patients with symptoms suggestive of acute cardiac ischemia (ACI). Capitalizing on the resources of two clinical effectiveness trials of ED decision making, the Acute Cardiac Ischemia Time Insensitive Predictive Instrument (ACI-TIPI) Impact Trial and the nearly completed Sestamibi Scan Clinical Trial, this project will determine whether agreement with guideline recommendations for triage is associated with decreased short-term rates of adverse outcomes (non-fatal myocardial infarction and death) and decreased short-term utilization (ED revisits, readmissions, coronary angiography, and revascularization). Through chart review, we will abstract items necessary to categorize 9191 study patients according to their risk of adverse short term outcomes, based on AHCPR triage guidelines and other unstable angina risk stratification models. For each guideline risk group, we will test the independent contribution of triage disposition to the prediction of adverse outcomes in hierarchical logistic regression models, controlling for the patient-level, physician-level, and hospital-level predictors of adverse outcomes. As unbalanced distribution of these predictors may bias comparisons of adverse outcome in "guideline- concordant" versus "guideline-discordant" triage disposition groups, we will examine two approaches for case-mix adjustment: propensity scores and ACI-TIPI scores. As several other existing instruments, in addition to guidelines, may improve decision-making in acute cardiac care, we will also compute the sensitivity and specificity of the guideline's risk groups in discriminating between patients with and without adverse short-term outcomes, compared to that of other available prognostic models for ACI. The proposed research will provide policymakers with the ability to project the impact of guideline implementation on outcomes, cost, and the use of health care services for patients with symptoms suggestive of unstable angina.